Can't connect to Postgres docker container from Golang container

Question

I have a web server built using golang. It works successfully when I test it locally.

However, when I build a docker image for my web server, it can't connect to a running Postgres container.

Here is my docker-compose.yml:

version: '2'
services:
    go:
        image: golang:1.7
        volumes:
          - ./:/server/http
        ports:
            - "80:8080"
        links:
            - postgres
            - mongodb
            - redis
        environment:
            DEBUG: 'true'
            PORT: '8080'

    postgres:
        image: onjin/alpine-postgres:9.5
        restart: unless-stopped
        ports:
            - "5432:5432"
        environment:
            LC_ALL: C.UTF-8
            POSTGRES_USER: user
            POSTGRES_PASSWORD: pass
            POSTGRES_DB: mydb
    mongodb:
        image: mvertes/alpine-mongo:3.2.3
        restart: unless-stopped
        ports:
            - "27017:27017"

    redis:
        image: sickp/alpine-redis:3.2.2
        restart: unless-stopped
        ports:
            - "6379:6379"

My Dockerfile:

FROM golang:1.7

RUN mkdir -p /home/app

WORKDIR /home/app

COPY . /home/app

RUN make deps && make

ENTRYPOINT ["./bin/api-test"]

EXPOSE 8080

The Postgres connection string I am using:

postgresql://user:pass@host/mydb?sslmode=disable

For host, I tried localhost and it returns the following error:

dial tcp [::1]:5432: getsockopt: connection refused

Tried postgres and it returns the following:

dial tcp 202.71.99.194:5432: getsockopt: connection refused

Tried the IP address I get running this command which returns 172.19.0.3:

docker inspect apitest_postgres_1 | grep IPAddress

where apitest_postgres_1 is Postgres container name. It also returned this error:

dial tcp 172.19.0.3:5432: getsockopt: connection timed out

Can you please tell me what I am missing here? I am inexperienced with docker and this took a long time investigating for a solution.

Edit: I run my golang docker using this command:

docker run --env-file ./example.env --rm -it -p 8080:8080  api-test

example.env is the file contains my environment vars.

Edit 2: I changed the connection string to the following:

postgresql://user:pass@postgres:5432?sslmode=disable

It returns the following error:

dial tcp: lookup postgres on 192.168.65.1:53: no such host

I'm getting the idea that my mac is the issue here. My default DNS is 8.8.8.8 which should not be a problem.

Answer 1

Looks like you're pulling go image instead of building you're own image.

Instead of image: golang:1.7 replace it with build: . to build and use your Dockerfile.

Also you might need to pass postgres environment variables DB_HOST, DB_USER, DB_PASS etc. you can achieve that but creating for example docker.env file and then add env_file under your go app docker-compose.yml file:

Example docker.env :

DB_HOST=postgres
DB_USER=user
DB_PASS=pass
DB_NAME=mydb

Corrected docker-compose.yml :

version: '2'
services:
    app:
        build: .
        volumes:
          - ./:/server/http
        ports:
            - "80:8080"
        links:
            - postgres
            - mongodb
            - redis
        environment:
            DEBUG: 'true'
            PORT: '8080'
        env_file: 
          - docker.env

    postgres:
        image: onjin/alpine-postgres:9.5
        restart: unless-stopped
        ports:
            - "5432:5432"
        environment:
            LC_ALL: C.UTF-8
            POSTGRES_USER: user
            POSTGRES_PASSWORD: pass
            POSTGRES_DB: mydb

    mongodb:
        image: mvertes/alpine-mongo:3.2.3
        restart: unless-stopped
        ports:
            - "27017:27017"

    redis:
        image: sickp/alpine-redis:3.2.2
        restart: unless-stopped
        ports:
            - "6379:6379"

Answer 2

In order to make a connection to postgres in docker compose becomes established, you need to replace localhost or 127.0.0.1 or postgres in your connection string with the name of the container being mentioned in your docker compose file.

For example, in your docker-compose.yaml file create database like this:

db:
    container_name: composepostgres
    image: postgres
    environment:

and then, in your code when creating your connection string, avoid using 127.0.0.1 or localhost or postgres, and instead use composepostgres in the place of them.

If not doing so, you will face with dial tcp 127.0.0.1:5432: connect: connection refused error.